In order to clarify the behavior of dissolved organic matters in river water, the Lake Tega-numa with the most accelerated water pollution in Japan and the River Ohhori with a remarkably great load of pollutants in its catchment area were chosen and variation in water quality and components of the dissolved organic matters in these areas were examined. Water sampling was made once every two weeks during the period June 1984 to December 1986. For analysis, each water sample was filtered with a 0.45 μm membrane filter to obtain the TOC and organic matters concentrations. From these results, the annual mean value of the soluble organic matters in the River Ohhori was 20.2 mg/l in the upper reach, 9.9 mg/l in the medium reach, and 7.7 mg/l in the lower reach. This tends to decrease from April to September and increase from October to March. The dissolved organic matters were comprised, for the dissolved-TOC, of proteins, 13.9-21.2% ; carbohydrates, 4.9-12.8% ; humic acids and fulvic acid, 9.6-19.9% ; tannin and lignin, 4.9-7.1% ; urea, 1.3-21.2% ; lipids, 3.6-8.9% ; anionic surfactants, 6.5-13.5% ; volatile organic acids, 5.6-7.2%, and unknown substances, 20.7-32.8%. The sum of the components of proteins, carbohydrates, volatile organic acids and anionic surfactants was 45.5% of dissolved organic matters as dissolved-TOC at station C and in the influent of municipal wastewater about 50%. As one of the causes of the pollution of the River Ohhori, the influx organic matters from the catchment area similar to those present in the municipal wastewater, may contribute greatly and the River Ohhori may be strongly affected by the urbanization of the surrounding area.